From 15b8a1751bd49a1c2e326bc49e643344f9b2c41b Mon Sep 17 00:00:00 2001
From: Vasiliy Vanchuk <v.vanchuk@tut.by>
Date: Tue, 8 May 2018 14:34:12 +0400
Subject: [PATCH] Add combinators

---
 src/ChurchNum.hs   | 6 ++++--
 src/Combinators.hs | 5 +++++
 2 files changed, 9 insertions(+), 2 deletions(-)
 create mode 100644 src/Combinators.hs

diff --git a/src/ChurchNum.hs b/src/ChurchNum.hs
index 0cc662a..f10ae44 100644
--- a/src/ChurchNum.hs
+++ b/src/ChurchNum.hs
@@ -13,6 +13,7 @@ module ChurchNum (
 ) where
 
 import           Base
+import           Combinators
 
 -- zero :: p2 -> t3 -> t3
 zero = Base.flip constant
@@ -21,8 +22,9 @@ zero = Base.flip constant
 one = apply
 
 -- two :: (t -> t) -> t -> t
--- @help: can't figure out point free version
-two x y = x $ x y
+-- @help: can't figure out point free version (cause s-combinator is not)
+-- two x y = x $ x y
+two = s Base.compose identity
 
 -- inc :: Num a => a -> a
 inc = (+1)
diff --git a/src/Combinators.hs b/src/Combinators.hs
new file mode 100644
index 0000000..88490ff
--- /dev/null
+++ b/src/Combinators.hs
@@ -0,0 +1,5 @@
+module Combinators where
+
+s f g x = f x (g x) -- S-combinator
+identity x = x -- I-combinator
+constant x y = y -- K -combinator